Predation of Daurian redstarts offspring in nest boxes by the Oriental magpie‐robin and tree sparrow

Abstract Birds select suitable nest sites for breeding to ensure their own and offspring's survival; however, they inevitably suffer some potential predation risk. We studied the breeding ecology of Daurian redstarts (Phoenicurus auroreus) by providing nest boxes for their breeding from March to August of 2022. We recorded the predation of both Daurian redstarts eggs or nestlings by Oriental magpie‐robins (Copsychus saularis) and tree sparrow (Passer montanus). Oriental magpie‐robin were recorded attacking a feeding female adult and depredating nestlings. After the nestling predation event, the Daurian redstarts abandoned the nest. This video evidence provide a better understanding of the potential predators of cavity‐nesting birds.


| INTRODUC TI ON
Predation is one of the most important selective pressures in nature, shaping evolutionary relationships in many systems including birds (Caro, 2005). The life history of all birds is characterized by a critical stage in which they are bound to a nest during the breeding period.
The selective pressures acting during this period probably modulate their biology to a large extent; thus, it is not surprising that nest predation is considered a key source of selection for birds (Martin, 1995).
Although the concealment and of cavity-nesting providing protection for cavity-nesting birds, nest predation remains a major cause of failure in their breeding process (Lima, 2009;Martin, 1993;Martin & Li, 1992). The species and kinds of nest predator depend on the geographical areas and habitat types (Shen et al., 2023). Therefore, the mode of predation and selective forces' pressures on nest sites may vary (Czeszczewik, 2004;Picman & Schriml, 1994). For example, some snakes can accurately swallow birds' eggs or nestlings in the nest (Gartner & Greene, 2008), and some raptors may prefer to attack the nestlings from outside the nest entrance using their beaks or claws when they catch the nestlings (Barnett et al., 2013;Suzuki & Ueda, 2013). Due to the constraint size of the cavity entrance, the predators of cavity-nesting birds mainly include some snakes, rodents, mustelids (Wesolowski, 2002); however, cavity-nesting birds as predators are rare, with some woodpeckers being reported in field (Wesolowski, 2002). Knowing the identity of predators and their mode of predation could help us to predict the prevalence of nest loss (Cox et al., 2012) and better understand ecological interactions and establish their conservation goals (Chalfoun et al., 2002;Lima, 2002). It also contributes to our understanding of the selection pressures that influence parental and offspring anti-predator strategies (Ibáñez-Álamo et al., 2015). However, the frequency and discreetness of natural predation events make it difficult for us to witness the predation process directly. Researchers often speculate about potential predators based on the remains (Williams & Wood, 2002), which may lead to the consequence that the actual nest predators are different from the predicted predators (Peterson et al., 2004). Miniature video cameras are widely used to monitor the behavior of breeding birds. For example, the video recording showed the process of multiple host individuals of the Oriental reed warbler (Acrocephalus orientalis) mobbing and at tacking a female common cuckoo (Cuculus canorus) in the field (Wang et al., 2020Zhao et al., 2022). In addition, the video cameras are able to accurately capture the process of nest predation cases (Ball & Bayne, 2012).
In this study, we recorded the whole process of Oriental magpierobins (Copsychus saularis) (hereafter OMR) and tree sparrow (Passer montanus) (hereafter TS) preying on the egg or nestling of Daurian redstarts (Phoenicurus auroreus) (hereafter DR) in next boxes. Here, we report this information in detail. The DR belongs to the order Passeriformes, family Turdidae, and is distributed in all provinces of China except Xinjiang, Tibet, and Qinghai. Its clutch size is usually 3-5, both male and female parents were involved throughout the brood (Figure 1). The DR usually nest in door joints, house pillars, road stone joints, and house wall joints, among other locations.

| MATERIAL S AND ME THODS
The study site was located in Liuzhi (26°10′-14′ N, 105°13′-24′ E, 1500 m in elevation), Liupanshui City, Guizhou Province, southwestern China. We studied the breeding ecology of DR by hanging nest boxes for them on trees or electric poles 3-4 m above the ground from March to August 2022. The entrance hole size of artificial nest boxes was 14 × 11 cm. The nest boxes have these dimensions: The height is 26 cm, on 12 × 12 cm. We used a miniature video camera (Uniscom-T71, 70 × 26 × 12 mm; Mymahdi Technology Co. Ltd.) to record the behavior of breeding birds during egg incubation and brood rearing. The miniature camera was mounted at the top, inside the nest box, and a mobile power supply (20,000 mAh, Romoss-Sense 6; Romoss Technology Co. Ltd.) was used to ensure all-day recording.
After the nest boxes were hung, they were all checked every 5 days.
Once a DR was found in a nest box, we numbered the nests and recorded the parameters of egg production and brood rearing.

| RE SULTS
In total, 143 nest boxes were suspended, of which 48 (36.5%) were used by breeding birds. Specifically, 28 (19.6%) were occupied by the OMR, 9 (6.3%) by the DR, 11 (7.7%) by the TS, and four (2.8%) by the Japanese Tit (Parus minor). Through video analysis, four DR nests were recorded as being predated by other cavity-nesting birds, of which three nests were predated by the OMR and one nest was predated by the TS.
At 9:59 h on July 4 (local time, Beijing, GMT+8), an OMR preyed on a DR egg, and the entire process took 7 s in R1 (Table 1;  In the face of intruders, parent DR birds showed nest defense behaviors. At 16:13 h on June 26, an OMR tried to invade the nest of a DR in R2. Coincidentally, a female Daurian redstart was feeding; thus, the DR and the OMR fought directly, and at the same time, a strong and noisy alarm sounded (detail in Video S5).

| DISCUSS ION
We incidentally observed that the OMR and the TS preyed on DR eggs or nestlings, of which one OMR attacked feeding DR and successfully preyed on DR nestlings in this study. All predations of DR nests were recorded on videos, adding to the compelling evidence of actual cases of nest predation in secondary cavity-nesting birds.
Japanese tit (Parus minor) has evolved a variety of nest defense behaviors to prevent their offspring and themselves from being harmed by predators, such as alarm calls, mobbing, and attacks (Yu et al., 2021). Similarly, DR showed alarm calls and nest defense behaviors to prevent their offspring and themselves from being harmed by predators (unpubl. data from our field observations). For many marshnesting blackbirds, predation is considered to be an important source of egg and nestling mortality (Ricklefs, 1969), the Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) has the similar encounter (Westneat, 1992). Predators can be responsible for most of brood F I G U R E 2 Diagram of the Oriental magpie-robin preying on the eggs or nestlings of Daurian redstarts (a, the female Daurian redstart incubating eggs; b, the Oriental magpie-robin preyed on one egg out of the nest box (details in Video S1); the red circle refers to the egg; c, the Oriental magpie-robin preyed on the 5-day-old Daurian redstart nestling from the nest box (details in Video S2); the red circle refers to the nestling; d, the Oriental magpie-robin entered the nest box and used its beak to peck the head of the common 3-day-old nestling of the cuckoo (details in Video S3); the red circle refers to the nestling).

F I G U R E 3
The tree sparrow preying on the egg of the Daurian redstart (a, the tree sparrow entered the nest box and used its beak to peck the egg; the red circle refers to the egg; b, one poked egg in the nest that was pecked by the tree sparrow (details in Video S4); the red arrow refers to the poked egg).